Ovarian Follicular Dynamics During the Luteinizing Hormone Surge in the Bottlenose Dolphin (Tursiops truncatus)

Abstract

Characterizing the relationship between ovarian follicular dynamics and the luteinizing hormone (LH) surge in the bottlenose dolphin (Tursiops truncatus) requires detailed daily monitoring due to the transitory nature of LH and ovulation. Utilizing conditioned dolphins and non-invasive sampling techniques, such as urine collection and trans-abdominal ultrasound exams, provides the means to accurately monitor these fleeting processes. Urine samples and ultrasound exams used in this study were originally performed for the purposes of artificial insemination and controlled natural breeding. The LH surge was identified by a rapid immunochromatographic assay (ICG), and real-time B-mode trans-abdominal ultrasound imaging was used to identify pre-ovulatory follicles (POF). Increases in urinary progesterone levels along with the disappearance of the POF verified ovulation. This study found that POF diameters during the LH surge were 1.942 +/-0.098 cm (n = 9), and time to disappearance of the POF from the last recorded LH peak sample was 37.475 +/-12.346 h (n = 6). Peak LH surge levels, based on samples collected 2 to 4 times daily, lasted 6.050 +/-1.332 h (n = 6). Data suggests that bottlenose dolphins, like many other mammals, have brief ovulatory LH surges followed by ovulation within 48 hours.